The only thing these communists understand is force.
Inform the North Vietnamese that they will surrender unconditionally within 7 days or Hanoi will be destroyed by an overwhelming nuclear strike. If they refuse, a city will be destroyed every three days until they agree to peace.
Nothing like genocide to get those damn commies to come to the negotiating table!
Better to render the country a smoking, irradiated crater than to see it enslaved to the forces of international communism.
So your solution is to risk global thermonuclear war?